Various methods are known for extracorporeal blood treatment, for example hemodialysis, hemofiltration, as well as a combination of these two methods, which is called hemodiafiltration. The extracorporeal blood treatment apparatuses have a blood treatment unit that is divided, by means of a semi-permeable membrane, into a blood chamber and a dialysis fluid chamber. During blood treatment, the blood of the patient flows in an extracorporeal blood circuit, through the blood chamber of the dialyzer, while dialysis fluid flows through the dialysis fluid chamber of the dialyzer in a dialysis fluid system. The extracorporeal blood circuit and the dialysis fluid system are referred to hereinafter, in general, as the fluid system of the extracorporeal blood treatment apparatus.
Peristaltic pumps are generally used for conveying the fluids in the fluid system in the extracorporeal blood treatment apparatuses, in which pumps at least one occlusion body moves along the elastic tubular line that serves as the pump chamber. These pumps are therefore also often referred to as occluding tube pumps. The most common occluding tube pump is a roller pump into which a section of the tubular line is laid.
However, extracorporeal blood treatment apparatuses are also known in which, instead of peristaltic pumps, non-occluding pumps, for example centrifugal pumps or impeller pumps are used, which do not have an occlusion body with which the tubular line is occluded.
Shutting off occluding pumps or reducing the speed of rotation of these pumps in the fluid system of the extracorporeal blood treatment apparatus proves to be non-problematic, in practice, because due to the occlusion body, there is no risk of reverse flow of the fluids. In the case of non-occluding pumps, in contrast, there is a risk that fluid, particularly blood of the patient, will flow counter to the conveying direction when the pump is shut off or its speed of rotation is reduced.